1. Field of the Invention
The present invention relates to an image scanning device able to handle paper fingerprint information.
2. Description of the Related Art
In recent years, digitalization is progressing due to the prevalence of technologies such as the Internet. Since a variety of information can now be readily acquired, it is essential for security technology to prevent information leakage and unauthorized use on information processing equipment.
In image processing devices such as photocopiers and Multifunction Peripherals, several technologies for guaranteeing that a document is the original are adopted as such security technology. One of these security technologies uses paper fingerprint information. Paper is made up of tangled plant fibers approximately 20 to 30 microns thick, and random patterns are created as a result of such tangling. These random patterns are called paper fingerprints, and like human fingerprints they differ for every single sheet of paper. Consequently, the authenticity of an original can be guaranteed by acquiring (i.e., registering) and verifying the paper fingerprint information thereof. The paper fingerprint information is acquired using an optical image scanning device housed inside an image processing device. The paper fingerprint information acquired by the scanning device is a shadow pattern of the plant fibers from a white region of the paper. In order to acquire the shadow pattern, the amount of light used to illuminate the document sheet when acquiring the paper fingerprint information must be less than (i.e., darker than) the amount of light used when performing regular image scanning. Thus, the gain adjustment values with respect to the image signal acquired when scanning paper fingerprint information are configured to be smaller than the gain adjustment values used when performing regular image scanning.
Meanwhile, scanning devices have been proposed wherein it is possible to use both a stationary document scanning method and a document feed scanning method (see Japanese Patent Laid-Open No. H07-110641, for example). The stationary document scanning method involves conveying and then stopping a document sheet on top of a document platen glass for documents, and subsequently causing an optical unit to be moved and scan an image. In contrast, the document feed scanning method involves holding the optical unit in place and scanning an image while conveying the document sheet. In an image scanning device wherein it is possible to use both the stationary document scanning method and the document feed scanning method, the user is able to select either of the document scanning methods by operating an operation unit of the image scanning device. In the case of the stationary document scanning method, in order to scan an image of the next document sheet after causing the optical unit to be moved and scan an image, the user must again return the optical unit to its original position. In contrast, in the case of the document feed scanning method, it is not necessary to return the optical unit to its original position because an image is scanned while conveying a document sheet, and thus the document scanning time can be shortened.
When scanning paper fingerprint information using the scanning device described above, the paper fingerprint information cannot be accurately scanned if rubbish or other material is adhering to the paper fingerprint information scanning region of the glass surface of the document platen upon which a paper sheet is placed. When scanning paper fingerprint information, the document sheet is illuminated with an amount of light that is less than (i.e., darker than) the amount of light used when performing regular image scanning. Consequently, it may become impossible to accurately scan paper fingerprint information due to the effects of tiny scratches on the surface of the glass plate or particles such as paper powder or dust adhering to the surface of the glass plate, even if the degree of such scratches or particles does not pose a problem during regular image copying. One method of coping with this problem is given in Japanese Patent Laid-Open No. 2005-038389, for example, which discloses a method for accurately scanning paper fingerprint information by scanning paper fingerprint information multiple times at different regions of the document platen, and then performing image processing (rotational and arithmetic processing) on the plurality of scanned data.
However, in the method disclosed in Japanese Patent Laid-Open No. 2005-038389, the user must place the document on the document platen oriented in a variety of angles (such as 0°, 90°, 180°, and 270°) in order to scan the paper fingerprint information at different regions of the document plate. For this reason, a large burden is placed on the user. Furthermore, device costs increase due to the need to provide functions in the scanning device for executing complex processing such as rotational processing and arithmetic processing.